1. Field of the Invention
The invention relates to a printing ink concentrate and a method for its production.
2. Discussion of Background Information
Printing inks are usually produced by combining the starting materials pigment, vehicles, additives and liquids and subsequent dispersion. The dispersion method is used to break up the pigment agglomerates into the necessary pigment particle size. The properties necessary for the printing ink, such as, e.g., sufficient coloring power and good printability, are thus achieved.
For a more rational and more economic manufacture of printing inks it is also customary to produce an intermediate in the above-mentioned production process. This intermediate is a printing ink concentrate that differs from the customary printing ink in that the pigment concentration is noticeably higher. The proportion of vehicles and liquids is therefore naturally lower. Printing ink concentrates are used to both produce finished printing inks and to increase the coloring material concentration of a printing ink of the same shade and for nuancing printing inks.
Vehicles and liquids are added to the printing ink concentrate for dilution, and the final printing ink is produced by a mixing method. A dispersion method is no longer necessary in the dilution stage, since the printing ink concentrate was produced through a dispersion step from the starting materials pigment, vehicles, additives and liquids.
Concentrates of printing inks therefore differ substantially from pigment preparations in that in a printing ink concentrate the pigments are already present in a dispersed form.
Printing ink concentrates are usually produced by dispersing solids, such as coloring pigments, and solid additives in vehicles and liquids with the aid of dispersion units such as triple-roll mills, kneaders, extruders or ball mills in several stages or in a single-stage process, as described in EP 0 807 670 A1.
With this method, viscous to highly viscous printing ink concentrates result that exhibit a tackiness.
The solids used are pigments, such as Phthalocyanine (CI 15), Pigment Red (CI 57:1), Diaryl Yellow (CI 12/13) and decorative ink pigments and other achromatic solids, also often called fillers, such as chalk, kaolin, butylated hydroxytoluene or dispersion additives. These are used in the form of powders or granules. The vehicles used can be varnishes for printing inks produced by boiling printing ink resins, printing ink oils and alkyds. Alkyds such as linseed oil alkyd, soybean oil alkyd are also used as vehicles. Special mineral oils for printing inks with a boiling range between 230-370° C., such as Printosol® C 800, and vegetable oils, such as linseed oil, soybean oil, are used as liquid components.
Flush pastes represent a form of printing ink concentrates produced in a different manner. They are likewise viscous to highly viscous and exhibit tackiness. Also in flush pastes the pigment is present in the ground fineness necessary for an application as printing ink and does not need to be further dispersed or finish-ground.
After manufacture, these printing ink concentrates are filled into transport containers, such as cans, buckets, drums, hobbocks or production containers. These are used for storing, transporting and for removing the printing ink concentrates.
To produce a finished printing ink, one or more printing ink concentrates are removed, weighed out and mixed, usually with the addition of additives, vehicles or liquid components, such as oils.
Weighing is usually carried out by the manual removal of the printing ink concentrates, e.g., with a spatula, and placement in a weighing container. Another method is represented by the use of so-called metering stations in which the printing ink concentrates are present in storage containers such as hobbocks or drums and are conveyed by means of pumps or hydraulic presses and are metered volumetrically or gravimetrically via metering valves. Such automatic installations are customary in the trade.
The weighed components are subsequently mixed to form the finished ink in mixers such as dissolvers, kneaders, blade mixers or other mixer units with the addition of additives, vehicles and oils. The mixing process serves to homogenize the product. A dispersion of the pigment is no longer necessary here, since this has already taken place during the production of the printing ink concentrate.
The high viscosity and tackiness of the printing ink concentrates represent a problem, especially depending on the pigment quantity used. The higher the proportion of pigment, i.e., the proportion of solids of the concentrate, the more viscous the product. Accordingly, handling, i.e., the manual removal or the pumpability of the printing ink concentrates, becomes more difficult.
A manual removal is often no longer possible. A product removal can only be carried out with considerable technical expense, e.g., by means of high-pressure presses, often assisted by heating the product.
While liquid printing inks can be pumped and conveyed and metered with relatively low expenditure, with pasty printing ink concentrates, complex and expensive suction pumps, such as helicoidal gear pumps or compressed air piston pumps, already have to be used. Due to the number of different shades that are necessary for producing special colors, usually 20 to 60 pump units are required for an automatic mixing plant, which represents a considerable expenditure.
At still higher viscosities of the printing ink concentrates hydraulic presses have to be used in order to achieve a still adequate conveying of the product. This high-pressure technique increases the expense by a multiple. As a rule, a manual removal, e.g., of such concentrates of offset printing inks is no longer possible at all.
It is desirable to overcome the described disadvantages of the prior art and at the same time provide a printing ink concentrate that can be easily transported and easily mixed with additional components.